One extensively used metallurgy for providing the ohmic contacts and interconnections in present integrated circuitry involves the use of a layer of a metal silicide, such as platinum silicide, in the contact holes which makes direct contact with the silicon substrate and a layer of aluminum over the platinum silicide. This layer of aluminum is in contact with a second aluminum layer pattern on the insulative layer over the semiconductor substrate which provides the interconnections. The reason that platinum silicide has been used in the contact holes is that aluminum has been found to make less than satisfactory direct ohmic contacts with silicon semiconductor substrates. Such platinum silicide contacts are also used to form Schottky barrier diodes.
Generally, in the process of forming the platinum silicide contacts, a relatively thin layer of a patterned dielectric or insulating film on a silicon semiconductor substrate is provided with contact openings in those areas where a contact to the silicon is to be formed. A thin layer of platinum is deposited over the entire surface by any conventional deposition technique, such as vapor deposition or sputtering. A short term heat treatment is then used to cause the platinum in the contact holes to combine with the silicon to form the platinum silicide. The uncombined platinum layer on top of the dielectric film must then be removed so as to retain the platinum silicide in the contact holes.
The removal of uncombined platinum has been conventionally accomplished by wet etching with etchants such as aqua regia. (See U.S. Pat. Nos. 3,271,286, 3,855,612, 3,956,527, 3,968,272 and 3,995,301). Drawbacks of the use of such etchants are the prospect of contamination by the various etchants, lack of any substantial differentiation in etching rates of the platinum and its silicide in the absence of an oxide layer, as well as associated handling, rinsing and drying operations.
The sputter etching of platinum has also been known (see for example, U.S. Pat. Nos. 3,271,286 and 3,975,252). The problem of similar sputter etch rates for platinum (about 95 A/min.) and platinum silicide (about 80 A/min.) has been improved upon by the process of U.S. Pat. No. 4,135,998 in which an increased differentiation of the sputter etch rate of platinum can be obtained, relative to the sputter etch rate of platinum silicide, by sputter etching in an ambient of a rare gas containing at least 1% by volume of oxygen or nitrogen, and preferably an ambient of argon containing 10% by volume of oxygen.